Homes are generally provided with several windows allowing sunshine into the home and allowing occupants to look outside the home. Double-hung sash windows are popular in the United States. Double-hung sash windows consist of two sashes contained in a rectangular frame. Often, at least the lower sash is movable in the vertical direction allowing one to open and close the window. Sashes usually consist of sash frame material, such as wood, surrounding several glass window panes. The bottom of the lower sash rests against a window sill. Window sills are often wood.
Wooden window frames and wooden sash frames and wooden window sills can shrink and swell with humidity changes and other weather changes. Window frames and window sills are also subject to wear, warpage, misalignment and the like. Thus, the place where the lower sash rests against the window sill is often not an air tight seal and drafts ensue. Such drafts can cause discomfort in the home and increase energy needs in heating and cooling the home.
The exterior of windows is often exposed to environmental elements including rain water, snow, sunlight, wind, and blown and splashed dirt.
Not all home occupants are home owners. Many people rent houses, apartments, condominiums and other structures as living space. Renters, and home owners in some situations, often prefer a removable appliance to address a draft through a window rather than repairing or replacing the window itself.